The effect of cigarette smoking on the cardiovascular system was determined in the following way: Two cigarettes of relatively high (1.54 mg) and very low (0.08 mg) nicotine content were smoked and compared to sham smoking, After inhalation under standardized conditions there was a relatively high increase of the plasma nicotine levels and a subsequent exponential decrease. Two hours after smoking the levels were still elevated. After 2 low nicotine cigarettes there was a significant small short-term increase. The changes of the pulse rate were directly related to the nicotine levels and the pulse pressure transit time from the heart to the calf and the digital blood flow was indirectly related to them. The regulation of these parameters is exactly related with the.nicotine levels probably through the release of catecholamines. The cardiovascular reactions after smoking may indicate the additional myocardial work load after cigarettes of different nicotine content.